JP2004-105360A discloses therein a conventional seat reclining apparatus for a vehicle, which inclines a seat back relative to a seat cushion. The seat reclining apparatus includes a ratchet having inner teeth, and a base arm attached with multiple poles to be movable in a radial direction. The ratchet is prohibited from rotating relative to the base arm with the inner teeth of the ratchet being engaged with outer teeth of the poles in response to the rotation of a cam provided around a rotational shaft, and the ratchet is allowed to rotate relative to the base arm with the inner teeth of the ratchet being disengaged from the outer teeth of the poles in response to the rotation of a cam provided around a rotational shaft. Accordingly, the pivotal rotation of the seat back relative to the seat cushion is prohibited and allowed, thereby adjusting or maintaining an inclining angle of the seat back at a required inclining angle appropriate to support an occupant seated on the seat cushion.
Each pole is guided to move in the radial direction with both side surfaces of the pole being slided on a pair of guides formed at the base arm. In JP2004-105360A, a surface of each guide, which faces the ratchet, is applied with a blanking process in a plate-thickness direction and is formed with multiple pole sliding surfaces in the plate-thickness direction. That is, JP2004-105360A suggests each guide having the multiple pole sliding surfaces formed in a stepped manner. In this case, the blanking or stamping amount of each pole sliding surface is reduced, so that the thickness of the connected portion of each pole sliding surface is increased compared with a conventional structure. Therefore, it is possible to enhance shear strength of each guide (connected portion) against a load applied from the corresponding pole while maintaining a conventional plate-thickness of the base arm.
Meanwhile, as described above, because the shear strength of each guide against the load applied from the corresponding pole is increased, the pole is supported by the guide more firmly in response to the increment of the shear strength. Therefore, for example when the seat back is exposed to impact, a sufficient amount of impact energy is not absorbed and an excessive amount of load may be applied to engagement portions of the inner teeth of the ratchet and the outer teeth of the pole. In this case, there is a possibility that the engagement may become unstable and the seat back may not be maintained at the required inclining angle stably.
A need thus exists for a seat reclining apparatus for a vehicle, which is not susceptible to the drawback mentioned above.